Simonim vs Divination

 Rabbeinu Bachya (Kad HaKemach Mezuza) This that there is a widespread practice not to marry except when the moon is full there is no prohibition in this custom since it is serves merely as a sign that the marriage should be good and successful. This is similar to our custom on the night of Rosh HaShanna. This is also like the custom of appointing kings next to a spring as a good sign that his kingdom be viable for a long time. Anyone who views the custom of marrying at the full moon  as anything other than more than a sign of success for the marriage makes it into darchei Emori